Not applicable.
This invention relates to a system for flaring biogas generated by landfill sites or waste water facilities, and, more particularly, to a system that decreases harmful combustion products.
In landfills and waste water treatment, oftentimes it is necessary to dispose of waste gases, such as methane, generated by the disposal and decay of biological products. Flaring systems are used to burn off or combust such biogases to prevent environmental, explosion, and worker safety hazards. Various flare units are utilized to combust the biogas. Assignee of this application manufactured a unit having a stack with a plurality of burners located therein. The burners are fed via a supply line containing biogas. The biogas is fed directly to the burners without any premixture of air. The tip of each of the burners is disposed in an aperture formed in a false bottom within a stack. The false bottom is insulated with refractory or other suitable heat-resistant material to ensure that excess heat generated by flames extending from the burner tip is not transferred to the burner manifold located below the false bottom within the stack. An annular gap exists between the burner tip and the aperture formed in the false bottom. Air from a chamber below the false bottom flows upwardly through these annular gaps and is utilized to accomplish the combustion of the biogas exiting the burner tip, and further to potentially quench the temperature in the stack if necessary to reduce and control the heat generated within the stack. The air is drawn into the chamber below the false bottom via dampers positioned in the outer wall of the stack. The dampers can be actuated to control the combustion and quench air that flows to the flame via the annular apertures in the false bottom.
This biogas flaring system suffers from various disadvantages. First, it is difficult to finely adjust the amount of combustion air utilized in the process by utilizing the air delivery structures of the prior art system. More specifically, a correct premixture of air and fuel, prior to combustion, can reduce the emissions of various harmful gases, such as nitric/nitrous oxide (NOx) and carbon monoxide (CO). The prior air supply structures do not allow a proper premixing of air with fuel prior to combustion. Further, if the biogas must seek combustion air within the stack, flames will often extend upwardly from the burner tip to substantial heights, thus requiring a substantial height of the stack to conceal the flames.
In prior systems, each flame generated by a burner tip is generally unrestricted after it exits the burner tip, and oftentimes flows in a nonturbulent manner. This type of flame structure can result in an unstable flare system which can generate a significant amount of combustion instability noise. Added to the noise generated by combustion instability is the noise of the quench air flowing through the blades of the dampers located in the stack wall of the prior art system.
Therefore, a flaring system is needed which alleviates the problems of the prior art discussed above.
Accordingly, it is an object of the present invention to provide a flaring system that reduces the emission of nitric oxide.
It is a further object of the present invention to provide a flaring system which reduces the emission of carbon monoxide even at lower combustion temperatures.
A still further object of the present invention is to provide a flaring system that decreases the flame length to decrease the size of stack required.
Another object of the present invention is to provide a flaring system that reduces noise resulting from combustion and noise resulting from air flowing across the damper blades and into the stack.
Yet another object of the present invention is to provide a flaring system that increases flame temperature resulting in an increase in destruction efficiency in unburned hydrocarbons.
Accordingly, the present invention provides for at least one burner for igniting a mixture of biogas and air. A main supply line supplies the mixture to the burner. A biogas supply line feeds into the main supply line. An air supply line also feeds into the main supply line. A mixer structure is utilized to ensure that the biogas and air are mixed prior to being supplied to the burner.
The invention also provides for a flame stability device for use in conjunction with the burner. The device includes an enclosure generally surrounding and extending upwardly from a burner tip. The enclosure has an inner surface that is exposed to a flame generated from the burner tip. A stability surface extends generally from the inner surface to the burner tip. The stability surface surrounds the burner tip and creates a turbulent zone also surrounding the burner tip. The flame generated by the burner tip reattaches to the inner surface above the stability surface.
The invention further provides for an ignition arrangement for a plurality of burners. The arrangement includes at least one enclosure surrounding one of the burners and extending upwardly from the burner tip. A pilot is used to ignite the enclosed burner. An ignition port extends from the enclosed burner to at least one adjacent burner such that when the pilot lights the enclosed burner, combustion gases from the enclosed burner travel through the ignition port to ignite the adjacent burner.
Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.